The invention is described in reference to color lithographic web presses but the method and apparatus may be used in aligning other types of web presses.
Two, three or four color posters, magazines, brochures and the like are commonly printed on a continuous web of paper that passes successively through a series of printer towers which, respectively, apply an image of one color. In order to print tonal variations and avoid overlapping color images on the paper, the print cylinders and image bearing plates must be in exact registry. Further adjustment may be required during the run as a result of wear on cylinders or image bearing plates or a change in paper characteristics which may result in wander and poor registration. Obtaining proper registration, however, is often a tedious and time consuming effort. In erecting the web press, the print towers are aligned and the spacing adjustment, and many web presses allow for longitudinal and lateral adjustment; however, many web presses have no mechanism for precision twist adjustment. The expense of press down time, in lost productivity, and the cost of keeping a press crew on the job during press set up is substantial. These expenses may make the difference between a profitable operation and a losing operation in a small print shop.
If a run requires a change of paper input roll, the registration process may have to be repeated and sometimes a change in paper characteristics requires registration adjustment during a run.
Most multi-color lithographic web presses used in specialty printing operations must be shut down to adjust orientation or twist adjustment. Due to frequent occurrence of erosion and errors in film stripping, plate making, plate bending and plate casting, variations in twist or orientation registration occur which, especially, in older machines results in interruptions in a run with production loss and time costs. Correcting twist errors is ultimately a trial and error process. Skilled pressmen may sometimes obtain correct registration on the first try; however, even the most skilled pressmen sometimes have to stop the press several times and make adjustments before proper registration is obtained.
While larger web presses and some newer small multicolor web presses are equipped with special mechanisms to adjust twist registration during operation, most small printing operations and many very substantial print shops still rely on web presses that cannot be adjusted while running.
It is an object of this invention to provide apparatus and a method for bringing images into registry while the web press is running. This invention is, in one sense, an improvement in web presses of the type that comprise multiple printing towers. In another sense, the invention is an apparatus and method that can be used with any web presses of the type referred to.
One of the important features of the invention is that it allows older web presses to remain competitive.